• The korean journal of orthodontics
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• v.32 no.2 s.91
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• pp.107-115
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• 2002

The aim of this study was to investigate experimentally the mechanical and histological effect of drilling process on the stability of micro-implant used for the orthodontic anchorage. For this purpose, 32 micro-implants(Osas$^{(R)}$, Epoch medical, ${\phi}$1.6 mm) were inserted into maxilla, mandible and palate in two beagle dogs. 16 micro-implants(8 per dog) were inserted after drilling with pilot drilling bur (drill method group). 16 micro-implants(8 per dog) were inserted without drilling (drill-free method group). After 1 week, micro-implants were loaded by means of Ni-Ti coil spring (Ni-Ti springs-extension$^{(R)}$, Ormco) with 200-300 gm force. Following 12 weeks, the micro-implants and the surrounding bone were removed. Before sacrifice, the mobilities were tested with Periotest$^{(R)}$(Siemens). Undecalcified serial sections with the long axis were made and the histologic evaluations were done. The results of this study were as follow ; 1. The osseointegration was found in both of drill-free method group and drill method group 2. Two of drill method group and one of drill-free method group in 32 micro-implants were lost after loading. 3. The mobilities of drill-free method group were less than drill method group 4. The bone contact on surface of micro-implants in drill-free method group was more than drill method group but there was no significant difference between groups. 5. The bone density in threads of micro-implants in drill-free method group was more than drill method group and there was significant difference between groups. These results suggest that drill-free method in insertion of micro-implants is superior to drill method on the stabilities, bone remodeling and osseointegrations under early loading.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.804-810
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• 1997

A new catalyst system composed of a main catalyst(copper chloride) and promotors of zinc chloride, tin, and cadminum showed excellent performances in the MCS synthesis from silicon and methylchloride. The mixture of catalyst/silicon(5/95), Zn/Cu=0.1, Sn/Cu=0.001, and Cd/Cu=0.001 was mixed in a slurry phase and activated into the contact mass, then it was used for MCS synthesis. The average selectivity was 92% at the silicon consumption of 92% and reaction rate was 175(g-MCS/hr.kg-silicon) at conversion of silicon.

• Composites Research
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• v.18 no.6
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• pp.9-18
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• 2005

With the wide applications of fiber-reinforced composite material in aero-structures and mechanical parts, the design of composite joints have become a very important research area because the joints are often the weakest areas in composite structures. This paper presents an analytical study of the stress distributions in mechanically single-fastened and multi-fastened composite laminates. The finite element models which treat the pin and hole contact problem using a contact stress analysis are described. A dimensionless stress concentration factor is used to compare the stress distributions in composite laminates quantitatively In the case of single-pin loaded composite laminate, the effects of stacking sequence, the ratio of a hole diameter and the width of a laminate (W/D ratio), the ratio of hole diameter and distance from edge to hole (E/D ratio), friction coefficient and clamping force are considered. In the case of multi-pin loaded composite laminate, the influence of the number of pins, pitch distance, number of rows, row spacing and hole pattern are considered. The results show that P/D ratio and E/D ratio affect more on stress distributions near the hole boundary than the other factors. In the case of multi-pin loaded composite laminate, the stress concentration in the double column case is better than the other cases of multi-pin loaded composite laminate.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.3
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• pp.89-95
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• 2022

In this study, glassy carbon coating was performed on the graphite using a phenolic resin and a curing agent was mixed with ethylene glycol as an additive to form the uniform surface. The phenolic resin was dried and cured under the environments of hot air, then converted into a glassy carbon layer by pyrolysis at 500~1,500℃. FTIR, XRD, SEM analysis, and density/porosity/contact angle measurement were performed for characterization of glassy carbon. The pyrolysis temperature for high-quality glassy carbon was optimized to be about 1,000℃. As the content of the additive increased, the effect of reducing surface defects on the coated surface, reduction of porosity, increase of contact angle, and increase of density were investigated in this study. The method of forming a glassy carbon coating layer through an additive is expected to be applicable to graphite coating and other fields.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.4
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• pp.97-104
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• 2010

In this paper, we provide an embedded type non-contact bio-radar heart and respiration rate monitoring system. We implemented the rate finding algorithm into the embedded system. The high-speed and reliable real-time signal processor is then tested. To avoid null-point data loss problem, we applied quadrature demodulation. Among several other combining techniques, we suggest arctangent demodulation for quadrature channel combining and DSP is used for real-time signal processing. We also suggest DC-offset compensation technique to preserve the wanted DC components of the IQ signals for accurate demodulation while keeping the dynamic range of the ADC lower. Using Texas Instrument C6711 series DSP and external 12Bit ADC, we implemented proper elliptic digital filter and autocorrelation detection algorithm for robust commercial hand held device.

• The Journal of the Korea Contents Association
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• v.14 no.4
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• pp.445-455
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• 2014

The purpose of this study is to examine what variables influence on teenagers' exposure to sexual content on their smartphone. For this, the present research used demographics, self-control, parental monitoring, conformity to peer groups, sensation seeking, differential association and media use as independent variables and applied survey method based on 449 teenagers. Main findings are as follows. First, male and high school students who have high school graduated father exposed to sexual content more, and the lower self-control and higher conformity to peer groups and differential association, the more exposed to sexual content. Second, male and high school students were intentionally exposing to sexual content more, and the lower self-control and higher differential association, the more intentionally exposing to sexual content.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.1
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• pp.185-190
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• 2020

The rapid aging is increasing as the shortage of medical facilities and the resulting of decline in the quality of public health. In order to ease the burden of rising medical expenses, advanced medical institutions are expanding their remote medical care to lower the cost of services. U-healthcare detects the changes in physical and chemical phenomena occurring in the human body and converts them into electrical signals that can be processed and feeds back to the results through analytical and visualization processes to select only the desired information from the measured signals. The service is provided through a process of providing an alarm to a user. However, traditional biometric methods of attaching sensors directly to the body can be annoying and rejected in daily life. Therefore, there is a need for a method of continuously measuring biometric information without causing inconvenience to daily life. In this paper, we propose an IR-UWB-based non-contact and non-responsive respiratory measurement system that can continuously monitor biological information without any inconveniences to daily life.

• Applied Chemistry for Engineering
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• v.20 no.1
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• pp.1-8
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• 2009

Bio-oil has attracted considerable interest as one of the promising renewable energy resources because it can be used as a feedstock in conventional petroleum refineries for the production of high value chemicals or next-generation hydrocarbon fuels. Currently, catalytic vapor cracking is considered the most potential upgrading method for stabilization of bio-oil, which is a pre-process required prior to feeding bio-oil into refineries. This review introduces the recent research and development trends on bio-oil upgrading via catalytic vapor cracking, focusing on catalysts and upgrading methods used.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.1
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• pp.14-20
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• 2003

Piezoelectric ultrasonic transducers for high temperature contact measurement were developed. These high temperature ultrasonic transducers (HTUT) consisted of bismuth titanate piezoceramic element whose Curie temperature is higher than $600^{\circ}C$, a backing material of the mixture of tungsten powder and inorganic binder, an inner alumina tube, a wear Plate and a housing. The operational frequencies or the HTUT were 1.04 and 2.08 MHz, respectively. Various commercially available couplants for high temperature were evaluated and compared. As a couplant for high temperature ultrasonic testing between HTUT and test specimen, gold epoxy was selected. The peak amplitude of pulse-echo signals from steel test specimen decreased with increasing temperature. The operational temperature of the HTUT reached up to $500^{\circ}C$ at which the continuous contact measurement was possible.

• Membrane Journal
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• v.16 no.2
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• pp.153-158
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• 2006

The crosslinked poly(vinyl alcohol) (PVA) mwmbranes with poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA) were used to measure the water vapor and air permeabilities at 25 and $35^{\circ}C$. In addition, the contact angles of crosslinked PVA membranes were observed and increased with PSSA-MA contents. The water vapor permeability of 15300 Baller (1 Baller=$10^{-10}cm^3(STP){\cdot}cm/cm^2{\cdot}s{\cdot}cmHg$) was shown the maximum value at $35^{\circ}C$ when PSSA-MA=7 wt% membrane was used. The gas permeability of 146 Barrer was indicated the maximum at PSSA-MA=7 wt% at $35^{\circ}C$ and $P(H_2O)/P(Air)$ was the highest value 109.2 at $25^{\circ}C$.